This invention pertains generally to medical implantable devices and particularly to spinal implants. Various devices for internal fixation of bone segments in the human or animal body are known in the art. The most common type of spinal implant system are hook and rod systems and pedicle screw systems which provides a means of gripping a spinal segment. However, both hook and rod and pedicle screw systems have limitations and are not appropriate for all types of spinal disorders.
Conventional hook and rod systems comprise a series of hooks and an elongate rod. Typically, the hooks are positioned against lamina which are not adjacent one another to decompress or compress a section of the spine. Further, the hooks are positioned before being connected to the connecting rod, requiring the surgeon to place each individual hook before attempting to mount the connecting rod onto the hooks.
A conventional pedicle screw system comprises a pedicle screw and a rod receiving device. The pedicle screw includes an externally threaded stem and a head portion. The rod-receiving device couples to the head portion of the pedicle screw and receives a rod (commonly referred to as a distraction rod). Two such systems are inserted into respective vertebrae and adjusted to distract and/or stabilize a spinal column. The pedicle screw does not, by itself, fixate the spinal segment, but instead operates as an anchor point to receive the rod-receiving device, which in turn receives the rod. One goal of such a system is to substantially reduce and/or prevent relative motion between the spinal segments that are being fused.
The implantation of pedicle screw systems are intricate, time consuming, and invasive into the spine of the patient. Typically, a series of pedicle screws must be carefully placed precisely in the narrow pedicle region of the spine. These pedicle screws are then fitted with rod receiving devices which are then in turn fitted with distraction rods. The system of screws and rods creates an intricate system for supporting the spine that takes considerable effort.
The placement of the screws and rods is time consuming because the components must be positioned through trial and error with repeated adjustment of position of the components until final proper positioning of all the components of the entire system is achieved simultaneously. Finally, the implantation of pedicle screw systems is highly invasive because screws must be deeply driven into the pedicle region of the spine within close proximity of the nerves of the spinal cord or spinal nerves branching off of the spinal cord. A more rapid and less invasive implantation system was sought to structurally support the spine especially in spinal stenosis patients where the settling of the spine causes impingement on the nerves yet the intervertebral discs remain largely intact.